Various different wired or wireless computer network systems and protocols exist for exchanging data between computing devices, nodes, connected to the network. Some network systems are based on using beacon signals in coordinating the data communication between the nodes. The beacon signal is generally a specific data transmission sent periodically carrying network specific information for the nodes connected or in vicinity of the computer network.
The problem and the current invention are relevant for many network systems. Let us consider an example: The Institute of Electrical and Electronics, IEEE, defines a standard for a wireless network 802.11 which is a set of medium access control (MAC) and physical layer, (PHY) specifications for implementing a wireless local area network, WLAN aka Wi-Fi. Another example of a standard defined by IEEE is 802.15.6 defining MAC and PHY specifications for packet-based short-range communications in a wireless body area network, WBAN. The MAC layer defines differentiated access phases for exclusive, scheduled and random access communication in a superframe-structured network, where a superframe is bounded by two beacon signals. In one superframe there can be maximum of two phases each (exclusive, scheduled and random access communication) and a contention access period. Structure of the superframe is explained in detail later on.
IEEE 802.15.6 defines two exclusive access phases, EAP, for highest priority communications.
One of the drawbacks of the solutions defined in the current standards is that those are not able to provide delay guarantees for time-critical applications, especially if a significant portion of the superframe duration is not reserved for EAPs. However, if long EAPs are allocated to the superframe but highest priority communications remain minimal or zero, there are less opportunities for other than the highest priority communications to access the medium, since only the highest priority communications are allowed to transmit during EAPs.
Current standards do not allow transmissions in the scheduled, but unused slots in the scheduled access phase. Z-MAC: a Hybrid MAC for Wireless Sensor Networks by Manesh Aia, Ajit Warrier, Jeongki Min, Injong Rhee, Department of Computer Science, North Carolina State University tries to solve the problem of allocated but unused slots by introducing a carrier sense multiple access, CSMA/time division multiple access, TDMA hybrid protocol for wireless sensor networks. According to the Z-MAC the nodes always perform carrier sensing and transmit only if the channel is clear. Slot owners are given a higher priority bit—they are given an earlier chance to transmit than non-owners. Therefore, if the slot owner does not have data to transmit, the non-owners can “steal” the slot by utilizing a contention-based CSMA channel access mechanism. Due the carrier-sensing feature the Z-MAC is suitable only for communication systems utilizing narrowband transmissions. Therefore it cannot be utilized as a general MAC layer scheme for standards utilizing broadband physical layers. Furthermore, the Z-MAC does not support application-prioritized traffic, such as highest priority transmissions.